Building images in CI pipeline in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to build a Docker image named 'myapp' using the Dockerfile in the current directory.

Docker

docker build -t myapp [1] Dockerfile .

Drag options to blanks, or click blank then click option'

A-f

B-d

C-b

D-p

Attempts:

3 left

💡 Hint

Common Mistakes

Using -d which is for detached mode in other commands.

Using -p which is for port mapping.

Using -b which is not a valid Docker build option.

The -f option specifies the Dockerfile to use. Here, it points to the current directory's Dockerfile.

2fill in blank

medium

Complete the command to push the Docker image 'myapp' to the Docker Hub repository 'username/myapp'.

Docker

docker [1] username/myapp

Drag options to blanks, or click blank then click option'

Arun

Bpull

Cbuild

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using pull which downloads images.

Using run which starts containers.

Using build which creates images locally.

The docker push command uploads your image to a remote repository like Docker Hub.

3fill in blank

hard

Fix the error in the GitHub Actions step to build a Docker image with tag 'latest'.

Docker

      - name: Build Docker image
        run: docker build -t myapp[1] .

Drag options to blanks, or click blank then click option'

A-latest

B:latest

C latest

D/latest

Attempts:

3 left

💡 Hint

Common Mistakes

Using a dash - instead of colon.

Adding a space before the tag.

Using a slash / which is for repository names.

Docker image tags use a colon : before the tag name, like :latest.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps branch names to their Docker image tags, only for branches starting with 'release'.

Docker

images = {branch: branch[1] 'v1' for branch in branches if branch.[2]('release')}

Drag options to blanks, or click blank then click option'

A+

B==

Cstartswith

Din

Attempts:

3 left

💡 Hint

Common Mistakes

Using == instead of startswith for string prefix check.

Using in which checks substring anywhere.

Using - or other operators instead of + for string join.

The + operator joins strings. The startswith method checks if a string begins with another string.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that maps service names (uppercase) to their version numbers, only if version is greater than 0.

Docker

service_versions = { [1]: [2] for [3], version in services.items() if [2] > 0}

Drag options to blanks, or click blank then click option'

Aname.upper()

Bversion

Cname

Dservice

Attempts:

3 left

💡 Hint

Common Mistakes

Using service instead of name as loop variable.

Not converting name to uppercase.

Using wrong variable names causing errors.

name.upper() converts the service name to uppercase for the key. version is the value. name and version come from iterating services.items().

Practice

1. What is the main purpose of building Docker images in a CI pipeline?

easy

A. To automate packaging the app for consistent deployment

B. To manually upload files to the server

C. To write application code faster

D. To monitor server health

Solution

1. Step 1: Understand CI pipeline role

   CI pipelines automate tasks like testing and packaging to ensure consistency.

2. Step 2: Identify Docker image purpose

   Docker images package the app and its environment for reliable deployment.

3. Final Answer:

   To automate packaging the app for consistent deployment -> Option A

4. Quick Check:

   CI builds images to package apps consistently [OK]

Hint: CI builds images to package apps consistently [OK]

Common Mistakes:

• Confusing image building with code writing
• Thinking CI uploads files manually
• Mixing deployment with monitoring

2. Which of the following is the correct command to build a Docker image named myapp with tag v1 from the current directory?

easy

A. docker build -t myapp:v1 .

B. docker create -t myapp:v1 .

C. docker run -t myapp:v1 .

D. docker push -t myapp:v1 .

Solution

1. Step 1: Identify Docker build syntax

   The correct syntax to build an image is docker build -t name:tag path.

2. Step 2: Match command to syntax

   docker build -t myapp:v1 . uses docker build -t myapp:v1 . which matches the syntax and current directory.

3. Final Answer:

   docker build -t myapp:v1 . -> Option A

4. Quick Check:

   Build command uses 'docker build -t name:tag path' [OK]

Hint: Use 'docker build -t name:tag path' to build images [OK]

Common Mistakes:

• Using 'docker create' instead of 'docker build'
• Confusing 'docker run' with building images
• Trying to push before building

3. Given this CI script snippet:

docker build -t myapp:latest .
docker tag myapp:latest myapp:build-123

What will be the result after running these commands?

medium

A. An error because tagging must happen before building

B. Only one image named 'myapp:build-123' exists

C. Two images: 'myapp:latest' and 'myapp:build-123' pointing to the same image

D. Two images with different contents

Solution

1. Step 1: Understand docker build output

   The build creates an image tagged 'myapp:latest'.

2. Step 2: Understand docker tag effect

   Tagging 'myapp:latest' as 'myapp:build-123' creates a new tag pointing to the same image.

3. Final Answer:

   Two images: 'myapp:latest' and 'myapp:build-123' pointing to the same image -> Option C

4. Quick Check:

   Tag duplicates image reference, no new image created [OK]

Hint: Tagging duplicates image reference, no new image built [OK]

Common Mistakes:

• Thinking tagging creates a new image
• Assuming error if tag after build
• Believing images have different contents after tag

4. A CI pipeline script has this line:

docker build -t myapp .

But the build fails with error: "Cannot locate Dockerfile". What is the likely cause?

medium

A. The tag name 'myapp' is invalid

B. Dockerfile is missing in the current directory

C. The docker daemon is not running

D. The build command syntax is wrong

Solution

1. Step 1: Analyze error message

   "Cannot locate Dockerfile" means Docker can't find the Dockerfile in the build context.

2. Step 2: Check build context and files

   Since the path is '.', Docker expects a Dockerfile in the current directory, which is missing.

3. Final Answer:

   Dockerfile is missing in the current directory -> Option B

4. Quick Check:

   Missing Dockerfile causes this error [OK]

Hint: Check Dockerfile presence in build directory [OK]

Common Mistakes:

• Blaming tag name for Dockerfile error
• Assuming daemon not running without checking
• Thinking build syntax is incorrect

5. In a CI pipeline, you want to tag Docker images with the build number stored in the environment variable BUILD_ID. Which command correctly builds and tags the image myapp with this dynamic tag?

hard

A. docker build -t 'myapp:${BUILD_ID}' .

B. docker build -t myapp:BUILD_ID .

C. docker build -t myapp:$(BUILD_ID) .

D. docker build -t myapp:$BUILD_ID .

Solution

1. Step 1: Understand shell variable syntax

   In shell scripts, environment variables are accessed with $VAR or ${VAR}.

2. Step 2: Identify correct variable usage in command

   docker build -t myapp:$BUILD_ID . uses $BUILD_ID which is valid and common in CI scripts.

3. Final Answer:

   docker build -t myapp:$BUILD_ID . -> Option D

4. Quick Check:

   Use $VAR to insert env variable in commands [OK]

Hint: Use $VAR to insert env variable in commands [OK]

Common Mistakes:

• Using literal 'BUILD_ID' instead of variable
• Using incorrect syntax like $(BUILD_ID)
• Forgetting to expand variable in tag